Research Looks at Cover Crops for Disease Control

HERSHEY, Pa. — Everybody’s heard of cover crops as a good source of nitrogen and a good way to cut down on soil erosion. But cover crops for disease control?

In an organic system, they could be a good, albeit costly tool.

At this week’s Mid-Atlantic Fruit and Vegetable Convention in Hershey, Tianna Dupont, sustainable ag educator with Penn State Extension, described research she’s been doing on the use of mustards, Sudan grasses and other cover crops to prevent soilborne diseases in organic vegetables.

Dupont said she got interested in the subject after hearing of increased problems with soilborne diseases in organic tomatoes and other vegetables.

Diseases such as Verticillium wilt in tomatoes, she said, can be challenging for organic growers to control, since they can’t fumigate like other, larger conventional growers do.

So she started researching alternatives and read about using various cover crops such as mustards, millets and flax as an alternative.

What she found was that some of these cover crops contain glucosinolates and enzymes that when crushed, create a chemical reaction that can be toxic to some diseases such as V. wilt.

She worked with a grower, Harold Weaver, owner of Meadow Gate Vista Farm in Bowers, Pa., on a study looking at a mustard cover crop planted before tomatoes, grown in a half-acre plot that had past problems with V. wilt.

The cover crop was planted in the spring of 2010, with seeding done at around 15 pounds to the acre using a spinner spreader.

A second crop was planted a few weeks later in a different location.

By early July, the cover crop was chopped up using a disc and flail mower.

She and Weaver later went in with a cultipacker to seal the area down.

The next spring, a V. wilt-susceptible variety of tomato was put in.

Dupont said she found that the disease did develop later in the season, with U-shaped lesions on the tomato leaves. But it wasn’t as prevalent as before and Weaver’s tomato production actually doubled.

“Statistically, there was a difference there,” Dupont said.

Weaver said he was skeptical at first when he looked through the plot in the summer of 2011. He said he saw V. wilt in many spots and didn’t think there was any impact at all.

A few days later, he went in with Dupont and took a closer look. The difference was visible in the number of plants that looked fairly good.

“We did see significant increase in production,” he said.

Still, he remains skeptical about whether the system can work on a year-to-year basis.

“The negatives are, it is pretty intensive. It’s an expensive process and it’s quite a commitment,” he said.

For one thing, Weaver said a grower should be set up for irrigation since the cover crop needs quite a bit of water. Dupont said Weaver watered the area every other day in the summer heat.

He said a grower also needs a flail mower or other type of tool or implement that can effectively chop the cover crop to a point where it can be incorporated into the soil.

Then there is the cultipacker, another tool needed to seal the area to prevent toxins from escaping into the atmosphere, although Dupont said watering can do the trick as well.

Probably the most important thing is the fact that Weaver had to take land out of production to accommodate the cover crop.

Dupont said a system like this isn’t for everyone, because of the time and costs involved.

When the crop is cut, she said, a grower should incorporate it almost immediately to avoid losing toxins to the atmosphere. She also said there should be about a two-week window at minimum between the cover crop and cash crop to ensure toxins are not left over that could damage the cash crop.

Picking a good, experienced seed breeder to work with is good, she said, considering they may have the seed you might be looking for.

“You want to make sure you pick varieties a breeder has worked with so they have more of it available to you,” she said.